1. Field of the Invention
The present invention relates to an improvement in electrochemical cell designed by enhancing manufacturing of a battery case, particularly a clam shell variety. A clam shell casing comprises two plate-shaped members, each having a surrounding rim mated to form the enclosure. More specifically, the invention is directed to a one-piece lid or header design containing a hermetic glass to metal seal (GTMS) for a terminal feed through and an electrolyte filling port. While particularly suitable for clam shell casing designs, the present one-piece lid is also useful other with casing constructions as well.
2. Prior Art
In prior and current product lines, the design of electrochemical cells includes a lid with separate ferrules or openings for providing a terminal pin feedthrough, and an electrolyte fill and closure mechanism. Designs for these functions usually consist of a lid, GTMS ferrule, and an electrolyte fill ferrule that are welded together to form a subassembly. This subassembly is further manufactured by having the GTMS inserted into its ferrule and the completed assembly is then welded into a battery case of various configurations. The battery is filled with electrolyte via the fill ferrule or area, and the fill mechanism is welded shut. In this embodiment, there are three components in the lid subassembly requiring four welds for completion.
Another prior art technique requires that the lid be of sufficient thickness to facilitate glassing and installing a fill closure directly into the lid without the provision of ferrules. However, this method has distinct disadvantages since the entire lid must be of increased thickness that in turn reduces the available internal volume of the cell. The prior art describes these various configurations.
For example, JP 406068861A shows a lid for a lithium battery that has a terminal feedthrough, a fill port, and a GTMS provided directly into the cell lid with no ferrules. The battery does not appear to be of a clam shell type. The thin case design of the clam shell would make adaptation of this technology very expensive and moreover, would not be adaptable to other battery configurations.
WO 92/10859 shows an electrochemical cell lid with a fill port as well as a terminal feedthrough. The GTMS is provided with a ferrule. However, while the fill port does not have a ferrule, there is an integrally machined boss portion for supporting a plug. Again, the casing is of a conventional prismatic shape, and not of a clam shell type. This type of fill arrangement is unsuitable for use with a clam shell design and further shows the need for the current invention.
U.S. Pat. No. 5,306,581 to Taylor et al. relates to a battery with a weldable terminal feedthrough including an insulator welded to an aperture in the header. The fill port includes a shaped portion of the lid extending downwardly into the interior of the casing and an integral upstanding ring surrounding the fill plug. Again, adaptation of this design to a clam shell case would be difficult, and resultantly very expensive.
Thus, as previously stated, the problem with the prior art lid or header designs is that a number of pieces need to be assembled and welded to create a hermetically sealed battery terminal feedthrough, and fill port. The new design, the subject of the current patent application, reduces the number of pieces required for a casing lid or header from three to one and reduces the number of welds required from four to two. The new design allows for greater flexibility in battery design while enhancing cell volumetric efficiency.